#!/usr/bin/env perl

use utf8;
use strict;
use 5.010;

binmode STDOUT, ':encoding(utf8)';

my $max_length = 20;

print "未定义的环境变量:\n";

printf "%${max_length}s\t+\n" => "-" x $max_length;

foreach my $word (sort keys %ENV){
	
#	print $ENV{word};

#	my $cond = $ENV{$word} // 'x';

	if(!($ENV{$word} // 'x')){
		printf "%${max_length}s\n" => $word;
	}
}
